He also discovered that a number of lizards, including iguanas,
bearded dragons, lace monitors and komodo dragons are venomous.
This new research indicates that when snakes first evolved 100
million years ago, their venom genes were already 100 million
years old. Snakes, the researchers found, are closely related
these lizards. It's only among these lineages that the researchers
have discovered venom. More distantly related lizards like geckos
and skinks have no venom genes.
Dr Fry said that because komodo dragons fed on carrion in the
wild, bacteria in their mouths had long been blamed for the pain,
swelling and prolonged bleeding that bites caused.
However, his doubts were raised after he saw a zoo keeper develop
symptoms too soon after being bitten for the effect to be put
down to bacteria. When he studied an Australian lace monitor, or
common goanna, the closest relative of the komodo dragon, he
found a gland running down the side of its jaw. Squeezing it
released the venom. Dr Fry's international team identified nine
toxins in lizard venom that snakes also produce. One toxin found
in the venom of the bearded dragon, one of the world's most
popular pet lizards, had previously only been identified in
rattlesnake venom.
But do not be alarmed bearded dragon, goanna and iguana lovers.
Your pets' venom is only present in small amounts and unlike
snakes; lizards have no fangs to inject the venom into their
prey.
It is believe that venom systems in reptiles evolved only once
about 200 million years ago, much earlier than had been thought,
in a common ancestor of snakes and lizards.
'The first venomous snake evolved from the heavy bodied swamp
monsters similar to the anacondas of today. They needed a new
tool to kill their prey since they were trading in the heavy
muscle in order to become quicker and more athletic. Enter venom.
They used this venom to feed on the cute little furry rodents
that eventually became us.', said Dr Fry.
"This origin of venom is so far back, that it occurred before the
snake we commonly think of as 'non-venomous' even showed up on
the tree of life. I realized that some of the ancient venom may
still be produced by them today. So I started looking at
non-venomous snakes. And when I looked at a ratsnake, the
archetypal non-venomous snake, I isolated typical cobra-style
toxin."
"I just wanted to see how far back I could take snake venom," he
said.
An international team of herpetologists collected cells from the
mouth secretions of wild and captive lizards and cataloged the
genes that were active in them.
After comparing these genes to those for snake venom they
"isolated some rattlesnake toxins from the bearded dragons and
started getting really excited," Dr. Fry said. As the research
progressed it turned up venom genes in other species.
Dr. Fry and his colleagues found that the proteins encoded in
these genes had the same effect as snake venom.
Whilst finding that lizards had similar venom was intriguing, it
did not solve the question of how and when it evolved. Scientists
have long debated which of the 4,750 species of lizards the
closest cousins to snakes are.
These discoveries helped two of Dr. Fry's colleagues, Nicolas
Vidal and S. Blair Hedges of Pennsylvania State University, who
had been working on a large-scale DNA study. "We finally got
enough data this year to resolve the problem," Dr. Hedges said.
The venom came first, snakes later.
The research led to new ways of classifying reptiles based on
their DNA and have found that the venomous snakes and lizards
branch from the same point. They proposed a new name for these
- Toxicofera - "those who bear toxins". This clade, or group,
now includes serpentes (snakes), iguaninae (iguanas), varanidae
(monitor lizards) and helodermatidae (Gila Monsters).
This discovery of the toxicity of many popular pet snakes is
likely to send shockwaves through the international pet snake
trade. Many non-venomous snakes, previously thought to have only
mild 'toxic saliva', actually have true venom. Dr. Fry's research
has shown that some of the snakes common in the overseas pet
market actually produce highly potent venoms.
This research highlights the misunderstanding that has often been
the case with reptiles. In the late-70s/early 80s, some of the
most popular snakes in the US pet trade were the Asian keelback
snakes. It was only after several children were bitten and became
severely ill that these snakes were found to be highly venomous.
"My research now shows that the vast majority of the snakes
commonly kept as pets are actually venomous. Are all these
species dangerous? Certainly not," Bryan says.
'Are there highly venomous species lurking in the petshops that
we don't know about? Definitely. I've consulted to two US
petshops where employees were paralysed after being bitten snakes
thought to be totally harmless.'
The discovery may even cause a legislative storm in the United
States and Europe.
However, it's not all doom and gloom. Lizard venom may prove very
useful in medicine. For some reason, the molecules in lizard
venom are much smaller than those in snakes. Small molecules are
less likely to be noticed by the immune system, meaning that they
are less likely to cause allergic reactions.
Unfortunately, even as scientists discover these promising drug
candidates, many of the lizards that produce them are threatened
with extinction. "These animals that could potentially have the
next wonder drug are literally getting wiped out before our
eyes," said Dr. Fry.
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